Ammo.js vs Cannon.js Architectural Differences

Choosing the right 3D physics engine for web-based applications often comes down to selecting between Ammo.js and Cannon.js. This article explores the primary architectural differences between these two libraries, comparing their compilation origins, memory management strategies, API designs, and feature sets to help you understand how they operate under the hood.

1. Compilation Origin: Ported vs. Native JavaScript

The fundamental architectural difference lies in how each engine was built:

• Ammo.js (Avoid Minimal Manual Operations) is a direct port of the Bullet Physics SDK, a highly industry-standard C++ library. It is compiled into JavaScript and WebAssembly (Wasm) using Emscripten. Because of this, Ammo.js benefits from the highly optimized, battle-tested algorithms of Bullet.
• Cannon.js is a native, lightweight physics engine written entirely in JavaScript from the ground up. It was designed specifically for the web, aiming for simplicity and a small footprint.

2. Memory Management

Because of their differing origins, the two engines handle memory in completely different ways:

• Ammo.js utilizes a WebAssembly heap. Because it is compiled from C++, it does not benefit from JavaScript’s automatic garbage collection for its internal physics objects. Developers must manually instantiate objects using helper methods and manually deallocate them using Ammo.destroy(object) to prevent severe memory leaks.
• Cannon.js is a native JavaScript library. It relies entirely on the browser’s automatic garbage collection. While this makes development much simpler and safer from leaks, frequent creation and destruction of physics bodies can cause garbage collection spikes, leading to occasional frame rate drops.

3. API Design and Developer Experience

The architectural source code directly impacts how developers interact with the APIs:

• Ammo.js exposes an API that closely mirrors C++ syntax. It requires verbose setup code, pointers (represented as memory addresses), and strict type matching. This creates a steep learning curve for developers accustomed to idiomatic JavaScript.
• Cannon.js features a clean, intuitive, and modern JavaScript API. It uses standard JS classes, vectors, and quaternions, making it incredibly easy to integrate with web rendering engines like Three.js.

4. Feature Set and Physics Fidelity

The depth of the physics simulation differs based on the maturity of the underlying codebases:

• Ammo.js inherits Bullet’s extensive feature set. It supports advanced rigid body dynamics, soft body physics (like cloth and ropes), complex collision shapes (convex hulls, heightmaps), and highly sophisticated constraints and vehicle physics.
• Cannon.js focuses strictly on essential rigid body dynamics. It supports basic shapes (spheres, boxes, planes, heightfields) and simple constraints, but lacks support for soft bodies, advanced friction models, and complex character controllers.

5. Performance and Execution Speed

While WebAssembly generally outperforms native JavaScript for heavy computation, the actual performance varies by use case:

• Ammo.js has a higher initialization overhead and a larger file size. However, once loaded, its WebAssembly-backed execution is significantly faster and more stable when handling hundreds of interacting rigid bodies.
• Cannon.js loads almost instantly due to its small file size and has lower overhead for simple scenes. However, its performance degrades faster than Ammo.js under high CPU stress or when managing complex collision meshes.